Phospholipid (PL) methyltransferase catalyzes the last two sequential methylations in the synthesis of phosphatidylcholine (PC) in the phospholipid biosynthetic pathway in yeast, Saccharomyces cerevisiae. The activity of this pathway in other eukaryotic membranes has been implicated in diverse functions such as a regulator of lipid composition, modifier of membrane fluid properties, and as a transducer of receptor mediated signalling. One objective of the research described in this proposal is to purify and characterize PL methyltransferase from yeast. In addition, the regulation and the mechanism of localization of PL methyltransferase will be studied using biochemical and yeast molecular genetic techniques. The structural gene, OP13, encoding this enzyme in S. cerevisiae has been isolated in the Henry laboratory. Antibodies will be used to develop protocols for purifying the native PL methyltransferase and for analyzing its localization within various compartments of t he yeast cell. In addition, the Schizosaccharomyces pombe homologue (CH01) to the S. cerevisiae OP13 gene has also been isolated in the Henry laboratory. An initial characterization of the S. pombe CH01 gene will be undertaken and used in a comparison study of PC biosynthesis and regulation in S. pombe and S. cerevisiae. Hopefully, the research proposed will lead to a better understanding of the function and regulation of the phospholipid methylation pathway in the synthesis of PC in yeast.